Frequency Modulation Nonlinear Correction and Ranging in FMCW LiDAR

The linearity of the laser frequency modulation is a crucial factor that affects the performance of the frequency-modulated continuous wave (FMCW) LiDAR ranging. Nonlinearity can influence ranging resolution and introduce errors. This paper proposes a method for correcting frequency modulation nonlinearity based on waveform preprocessing for the modulation signal of the laser. After correction, the residual nonlinearity (1-r2) of the laser is reduced to $1.85\times 10^{-4}$ for the up-sweeping and $8.47\times 10^{-4}$ for the down-sweeping using the modulation signal with the repetition frequency of 50 kHz. The full-width at half of the maximum (FWHM) of the spectrum decreases by 86% compared to pre-correction, resulting in the ranging error of 0.37% at the distance of 38 cm. With distances of 0.90 m, 1.80 m, 2.89 m, and 4.13 m, respectively, the ranging error stabilizes at 0.2%, and the minimum deflection of distance can reach $8~\mathrm {\mu m}$ .